Spinal implant systems provide a rod for supporting the spine and for properly positioning components of the spine for various treatment purposes. Bolts, screws, and hooks are typically secured to the vertebrae for connection to the supporting rod. These vertebral anchors must frequently be positioned at various angles due the anatomical structure of the patient, the physiological problem being treated, and the preference of the physician. It is difficult to provide secure connections between the spinal support rod and these vertebral anchors at all the various angles that are required, especially where there are different distances between the rod and bolts and where these components are located at different heights on the patient.
One solution to this problem is shown in U.S. Pat. Nos. 5,643,263 and 5,885,285 to Simonson, the disclosures of which are specifically incorporated into this specification by reference. These patents describe a connection between a rod and a vertebral anchor, through which a surgeon may vary the angle between a spinal rod and the anchor to which the rod is attached. The connection is equipped with an interlocking set of washers that allow the surgeon to fix the desired angle between the anchor and the rod. In general, this system requires the surgeon in a typical installation to either sacrifice the capsule of the facet joint that may reside next to the connection, or elevate the connection above the facet joint and thereby raise the profile of the entire spinal implant system at that location. Occasionally, however, the surgeon may not wish to exercise either of these options in a particular surgery. Hence, an improvement over the device shown in these earlier patents would be a connection assembly that simultaneously minimizes the profile of the spinal implant system above the patient's spine without generally requiring the surgeon to sacrifice a facet joint that may reside next to a particular rod-to-vertebral-anchor connection assembly. The following invention is one solution to that need.